Learn More about Mercury

Mercury, also called quicksilver, is a chemical element in the periodic table that has the symbol Hg (from the Greek hydrargyrum, for watery (or liquid) silver) and atomic number 80. A heavy, silvery, transition metal, mercury is one of only two elements that are liquid at room temperature (the other is bromine). Mercury is used in thermometers, barometers and other scientific apparatuses. Mercury is mostly obtained by reduction from the mineral cinnabar.

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Occurrence In The Environment

Preindustrial deposition rates of mercury from the atmosphere may be in the range of 4 ng/L in the western USA. Although that can be considered a natural level of exposure, regional or global sources have significant effects. Volcanic eruptions can increase the atmospheric source by 4–6 times.

Mercury enters the environment as a pollutant from various different industries:

coal-fired power plants are the largest source (40% of USA emissions in 1999, which have since declined by 85%).

industrial processes

chlorine, steel, phosphate & gold production

metal smelting

manufacture & repair of weather and electronic devices

incineration of municipal waste streams

medical applications, including vaccinations

dentistry

cosmetic industries

laboratory work involving mercury or sulfur compounds

Mercury also enters into the environment through the disposal (e.g., landfilling, incineration) of certain products. Products containing mercury include: auto parts, batteries, fluorescent bulbs, medical products, thermometers, and thermostats. Due to health concerns (see below), toxics use reduction efforts are cutting back or eliminating mercury in such products. For example, most thermometers now use pigmented alcohol instead of mercury. Mercury thermometers are still occasionally used in the medical field because they are more accurate than alcohol thermometers, though both are being replaced by electronic thermometers. Mercury thermometers are still widely used for certain scientific applications because of their greater accuracy and working range.

One of the worst industrial disasters in history was caused by the dumping of mercury compounds into Minamata Bay, Japan. The Chisso Corporation, a fertilizer and later petrochemical company, was found responsible for polluting the bay from 1932–1968. It is estimated that over 3,000 people suffered various deformities, severe mercury poisoning symptoms or death from what became known as Minamata disease.

Health and Environmental Effects

Elemental, liquid mercury is slightly toxic, while its vapor, compounds and salts are highly toxic and have been implicated as causing brain and liver damage when ingested, inhaled or contacted. The main dangers associated with elemental mercury are that at STP, mercury tends to oxidize forming mercury oxide, and that if dropped or disturbed, mercury will form microscopic drops, increasing its surface area dramatically.

Mercury is a bioaccumulative toxin that is easily absorbed through the skin, respiratory and gastrointestinal tissues. Inorganic mercury is less toxic than organic compounds (molecules containing carbon). Even though it is far less toxic than its organic compounds, elemental mercury still poses significant environmental pollution and remediation problems due to the fact that mercury forms such organic compounds inside living organisms.

One of the most dangerous mercury compounds, dimethylmercury, is so toxic that even a few microliters spilled on the skin can cause death. One of the chief targets of the toxin is the enzyme pyruvate dehydrogenase (PDH). The enzyme is irreversibly inhibited by several mercury compounds, the lipoic acid component of the multienzyme complex binds mercury compounds tightly and thus inhibits PDH.

Minamata disease is a form of mercury poisoning. Mercury attacks the central nervous system and endocrine system and adversely affects the mouth, gums, and teeth. High exposure over long periods of time will result in brain damage and ultimately death. It can pose a major health risk to the unborn fetus. Air saturated with mercury vapor at room temperature is at a concentration many times the toxic level, despite the high boiling point (the danger is increased at higher temperatures).

Through bioaccumulation, methylmercury in the environment works its way up the food chain, reaching high concentrations among populations of some species such as tuna. Mercury poisoning in humans will result from persistent consumption of tainted foodstuffs. Larger species of fish, such as tuna or swordfish, are usually of greater concern than smaller species, since the mercury accumulates up the food chain.

Watersheds tend to concentrate mercury through erosion of mineral deposits and atmospheric deposition. Plants absorb mercury when wet but may emit it in dry air. [4] Plant and sedimentary deposits in coal contain various levels of mercury.

Ethylmercury is a breakdown product of the antibacteriological agent thimerosal which has effects similiar but not identical to methylmercury.

Precautions and Regulations

Mercury should be handled with great care. Containers of mercury need to be covered securely to avoid spillage and evaporation. Heating of mercury or mercury compounds should always be done under a well-ventilated, filtered hood. Additionally, some oxides can decompose into elemental mercury, which immediately evaporates and may not be apparent.

Due to the health effects of mercury exposure, industrial and commercial uses are broadly regulated in Western countries. The World Health Organization, OSHA, and NIOSH, all agree that mercury is an occupational hazard and have established specific occupational exposure limits. Environmental releases and disposal of mercury is regulated in the U.S. primarily by the EPA.

In recent years, governments have issued warnings that certain fish in excess quantities are unsafe due to methylmercury levels (death has been known to occur from mercury contaminated fish). Such warnings especially target pregnant women.

The Clean Air Act, passed in 1990, put mercury on a list of toxic pollutants which need to be controlled to the greatest possible extent. Thus, all industries that emit mercury into the environment must install maximum achievable control technologies (MACT). However, a March 2005 EPA rule took power plants off the list of sources which must reduce mercury to the maximum extent. Instead, a cap and trade rule, which would not reduce mercury pollution from power plants at all until the year 2018, was issued. That rule is thought to be illegal and is being challenged by at least 13 states in court.